The structure of aqueous cadmium sorption complexes on the iron oxyhydroxide minerals goethite (~-FeOOH), lepidocrocite (?-FeOOH), a k a g a n e i t e ( ~ F e O O H ) , s c h w e r t m a n n i t e (FesOs(OH)6SO4), and cryptomelane (KMn8OI6) have been determined in situ (in the presence of water) using Extended X-Ray Adsorption Fine Structure (EXAFS) spectroscopy. Sorption on these minerals may limit the mobility of Cd in soils and groundwater.